General Sir Richard Barrons gave his warning during a hearing of the UK parliamentary defence committee. The former head of the Joint Forces Command was asked on Tuesday to explain at what point NATO would have no choice but to fight Russia.
Members of the alliance have been providing aid to Ukraine since the beginning of the conflict through providing weaponry, finance, and other key supplies, but have made a concerted effort to avoid direct action in the conflict.
NATO was set up in the aftermath of the Second World War and its 30 members have all agreed to mutual defence in the event of an attack from a non-member country.
The formation of the alliance based on defence means that with the invasion of Ukraine, a non-member country, NATO has no place directly defending the nation without escalating the conflict.
General Barrons stated that the organisation “will have a call to make” in the event that Russian forces begin to succeed on a larger scale and target larger parts of Ukraine.
He added: “And that call would be easier if we had made any preparations at all to act in those circumstances at the speed required, and we have not.”
The General was asked what other scenarios in relation to the conflict in Ukraine would lead to NATO involvement.
He said: “The second aspect would be if whatever happens in Ukraine causes President Putin to escalate it for his own purposes into other parts of NATO.
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Sweden and Finland share borders with Russia and have expressed their interest in joining NATO, despite a warning from Putin of the dangers of escalation in the event of their membership.
President Putin labelled the alliance as “a tool geared towards confrontation” and noted that the membership of Sweden and Finland “will not bring stability to the European continent”.
During NATO’s summit in the summer, the General said that the priority should be “to reset the balance of power with Russia” in terms of military capability so Moscow “no longer thinks it can set the terms of debate with NATO”.